He's a better asset in terms of surplus value, but not in terms of tempo. By basic surplus value analysis trading an 8 win player who makes $10M with one year of control for 12 one win players making the league minimum with full control might even make sense, even though it defies common sense. One elephant sized chicken would defeat ten thousand chicken sized elephants.
Boston just shaved like ~4 marginal projected wins off of their competitive 2020 roster. There is a huge cost to that and it's not captured by basic surplus value analysis.
That aside, I agree that the "bad for baseball" takes are largely bellyaching. The superstar went from one rich team to another; collectively baseball is just as good and the owners are paying out just as much salary. It's s***** for Red Sox fans is what it is.